Are two spaces better than one? | Butterick’s Practical Typography

Be cause the study costs $39.95 for a PDF, I’m certain the social-me dia skep tics rush ing to claim vic tory for two-spacing have neither bought it nor read it. But I did both.

And read it. Key result:

….. researchers found that putting two spaces after a period de livered a “small” but “statistically … detectable” improvement in reading speed—about 3%

3% improvement could easily have been achieved with a better font.

The paper tells us that the paragraphs were set in “14 point Courier New font” with “quadruple” line spacing, which I’ll take to mean quadruple the point size = 56 point. The authors don’t mention how wide the lines were, nor the color of the type, nor the back ground (though these decisions would also affect readability).

He goes on to make the point that readability is based on many factors. For example, the Courier font was designed for use on IBM typewriters and renders badly on old CRT displays. Consider when the ball strikes the ink ribbon on the paper that considerable spreading of ink occurs making a thicker, bolder output. On computer screens, the older Courier font is too thin and almost unreadable for many people.

The para graphs were not printed, but rather displayed on a “21 inch NEC Accusync 120 monitor” running Windows (version not specified). This CRT display, first made in 2002, supports a maximum 1600 × 1200 resolution. CRTs, however, can be operated at multiple resolutions, and the paper doesn’t mention exactly which was used—an other decision that would affect readability, since it would change the apparent size of the font. Still, pretty much what you’d expect to find in the psychology lab of a liberal-arts college—equipment handed down two up grade cycles ago—though not what most readers are us ing today.

From my view, this invalidates the entire test. CRT displays with fuzzy resolution are rendering a legacy font designed for typewriters and results show a 3% improvement.